全文获取类型
收费全文 | 7218篇 |
免费 | 643篇 |
国内免费 | 1083篇 |
出版年
2024年 | 27篇 |
2023年 | 218篇 |
2022年 | 167篇 |
2021年 | 271篇 |
2020年 | 298篇 |
2019年 | 371篇 |
2018年 | 258篇 |
2017年 | 294篇 |
2016年 | 308篇 |
2015年 | 278篇 |
2014年 | 324篇 |
2013年 | 503篇 |
2012年 | 298篇 |
2011年 | 345篇 |
2010年 | 259篇 |
2009年 | 365篇 |
2008年 | 320篇 |
2007年 | 375篇 |
2006年 | 384篇 |
2005年 | 376篇 |
2004年 | 309篇 |
2003年 | 278篇 |
2002年 | 241篇 |
2001年 | 197篇 |
2000年 | 212篇 |
1999年 | 195篇 |
1998年 | 152篇 |
1997年 | 121篇 |
1996年 | 124篇 |
1995年 | 108篇 |
1994年 | 109篇 |
1993年 | 104篇 |
1992年 | 116篇 |
1991年 | 89篇 |
1990年 | 68篇 |
1989年 | 62篇 |
1988年 | 50篇 |
1987年 | 46篇 |
1986年 | 34篇 |
1985年 | 48篇 |
1984年 | 41篇 |
1983年 | 20篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1974年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有8944条查询结果,搜索用时 187 毫秒
61.
Learning methods developed by artificial intelligence research teams are very efficient for biological sequences analysis but they need running on large computers accessed by terminals. These computers are interfaced with standard displays involving long and unpleasant alphanumerical data handling. The "biological work station" is a personal computer with a color graphic screen providing a user-friendly interface for the artificial intelligence learning programs running on large computers. It provides to biologist a graphical convenient tool for sequence analysis built with efficient man-machine communication methods such as multiwindows, icons and mouse selection. It allows the biologist to edit and display sequences in an efficient and natural way, showing off directly on color pictures the data and the results of learning programs. 相似文献
62.
It is sometimes necessary to identify eitherH. bulbosum orH. murinum on the basis of the inflorescence or seeds alone. The majority of taxonomic keys use the presence of swollen basal culms for the former against the annual habit for the latter. Confusion is due to similarities in inflorescences and spikelet morphology. Lodicules which always persist and are present beside the fruit in a mature caryopsis, and other characters such as the awns of the lemmas of the lateral spikelets enable conclusive distinction. 相似文献
63.
Christian Leuckert 《Plant biology (Stuttgart, Germany)》1985,98(1):401-408
Die Kombination (Koppelung) der Stoffe im Chemosyndrom kann gegenseitig oder einseitig obligat oder auch fakultativ sein. Dabei ist die Stellung der beteiligten eng verwandten Produkte im Rahmen der Biosynthese von Fall zu Fall verschieden. — Dem Chemotaxonomen kann die Berücksichrigung dieser Aspekte zumindest tendenziell als Anhaltspunkt dienen. Bei Vorkommen der Komponenten in verschiedenen Verwandtschaftskreisen wird man ein Chemosyndrom - also eine Kornbination biogenetisch eng verwandter Verbindungen - urn so eher als ein einziges Merkmal betrachten können, je seltener die Kombination aufgelöst ist. Zweifellos stellen der solitare Stoff als Einzelmerkmal und die ohne Ausnahme auftretende (obligate) Kombination als Einzelmerkmal nur Extreme einer gleitenden Reihe dar. Herrn Prof. Dr. E. KLUG (Berlin) danke ich für die Durchsicht des Manuskripts und für werrvolle Diskussion, Herrn H. LÜNSER für die sorgfältige Ausführung der Zeichnungen, Frau I. EGGERT, Frau C. MÜLLER und Frau 1. POHL für die Hilfen bei der Vorbereitung des Manuskripts. Herrn Dr. M. SEAWARD (Bradford) bin ich für Beratung und Diskussion in Zusammenhang mit der Form der englischen Zusammenfassung sehr zu Dank verpflichter, 相似文献
64.
During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism.
Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but
not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton
since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite
were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher
levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied,
particularly the pyrethroids.
Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept.
of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. 相似文献
65.
66.
Paton G., Thomas R. J. and Waller P. J. 1984. A prediction model for parasitic gastroenteritis in lambs. International Journal for Parasitology14: 439–445. The parasite Ostertagia circumcincta is a major cause of parasitic gastro-enteritis in lambs in temperate countries. A prediction model is described, based on a mathematical representation of the external and internal stages of the life-cycle.The model is used to predict the numbers of infective larvae on a permanent experimental paddock grazed by ewes and lambs in 1973 and 1974. The “moisture status” of the surface layer of the pasture was found to be of fundamental importance for the successful prediction of the development and survival of the pre-infective larval stages. For the years studied the contribution to the summer wave of infection by lamb derived larvae was particularly significant. 相似文献
67.
Experiments were conducted to quantify parasitism of Colorado potato beetle,Leptinotarsa decemlineata (Say), by the egg parasitoid,Edovum puttleri Grissell, on 3 different cultivars of eggplant,Solanum melongena L. Levels of parasitism were higher (P<0.05) on ‘Black Pride’ than on other cultivars. The percentage of egg masses that
were parasitized was 1.2-fold higher (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’. The number of eggs per
mass that were parasitized was 1.3- and 1.4- fold greater (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’,
respectively. The percentage of eggs that were parasitized per mass and percentage of emerged adult parasitoids did not differ
(P>0.05) among cultivars; between 2.1- to 2.6- fold more females than males emerged from eggs on all cultivars during the
growing season.Edovum puttleri suppressed the 2nd generation ofL. decemlineata on ‘Black Pride’ and ‘Harris Special’, but did not suppress populations on ‘White’.
相似文献
68.
Arrhenotokously reproducing Hymenoptera and Acarina include many important natural enemies. This reproductive system offers
the opportunity of selection on hemizygous (♂ ♂), with the attendant advantages of an unmasked genotype fully exposed to selection,
in creased frequency of genotypes expressing rare genes, and enhanced discrimination of characters, in all-♂ populations produced
by virgin (♀ ♀). Increased selection intensity and reduced genetic drift may offer additional advantages. The method is limited
to characters displayed by (♂ ♂), and may require labor-intensive techniques and species-specific research. The method has
been shown to be practicable withAphytis holoxanthus DeBach (Hymenoptera: Aphelinidae), an important parasite of the Florida red scale,Chrysomphalus aonidum (L.) (Homoptera: Diaspididae).
相似文献
69.
The identification and efficiency of arthropod predator and parasites related to natural control of cotton leafworm eggs,Alabama argillacea (Huebner), were studied in a cotton field, Jaboticabal, SP, Brazil. Plants were marked randomly and the eggs found on them were indicated by arrow tapes for predation and parasitism observations. To evaluate and identify the arthropod fauna in the row-meter containing the marked plant, visual countings and collections using D-Vac ® and “beat sheet” were used. The average predation rate during the season, in the presence of 23.0 predators per row-meter, was 50.6% and the parasitism byTrichogrammatoidea annulata was 44.9% totaling 95.5% of egg reduction. In decreasing order of abundance, the arthropod predators found were the antPheidole sp., the spiderChrysso clementinae Petrunkevitch, the hemipteraOrius insidiosus Say andCeratocapsus mariliensis Carvalho & Fontes, and the coccinellidHyperaspis festiva (Mulsant). 相似文献
70.
似鳡属(Luciocyprinus Vaillant)是鲤科鱼类中属于鲃系(陈湘粦等,1984)的一个属,下咽齿3行,臀鳍无硬刺,具分枝鳍条5根。过去只记载一个种,外形很像鳡鱼,是由于摄食习性相同而导致的趋同现象(林人端,1981),故称似鳡,在广西俗称墨线鳡,云南俗称杆条鱼。分布于西江水系,包括云南中南部的湖泊,与鳡鱼分布于同一水系,但各占一定的水域,互不重叠。 关于似鳡的拉丁名称,惯用Fustis vivus Lin,是林书颜1932年定的新属新种, 相似文献